The head of the teachers union warned yesterday that the Board of Education won’t be able to attract enough teachers for its massive summer-school program without raising their pay.

United Federation of Teachers president Randi Weingarten also said the ambitious program for failing students could flop because City Hall and school officials are dragging their heels on negotiating the terms.

The board has estimated it will need 17,000 teachers for its expanded mandatory summer school program. Officials predict as many as 320,000 failing students will have to enroll.

Weingarten said it would be “irresponsible” for her to call on teachers to sign up while details are sketchy.

“I’ve been knocking on the door at the Board of Education to find out what the program will look like,” she said.

The nearly 12,000 teachers who worked last summer earned about $32 an hour. That’s not enough, Weingarten said, adding, “We had a hard time getting people.”

A top aide to Mayor Giuliani said the city is willing to negotiate a raise — under certain conditions.

City Hall has set aside $160 million for summer school, nearly twice as much as last year, but wants 20 percent of the money used to hire outside companies or private schools. The board has called for bids.